That is the messed up part for me, I'll equip the knife walk up behind someone, attempt take down and the dude like pulls the knife back as if he's going to stab but never does. So it just sits in that cocked position and stays retarded

If you're bbehind them standing with your knife out like an idiot after trying to action knife them, press and hold knife button and it will action knife (and leave you with the knife out after the kill)